Conventionally, telephony users received a direct connection to the Central Office (CO) as shown in FIG. 1. For example, the CO 500 can be connected to an analog telephone 502, to analog conference call equipment 503, to analog headset equipment 505, to an analog facsimile (fax) machine 504 or to an analog modem of a computer 506.
Many users of telephony equipment utilize a PBX to provide convenience or enhanced features or both over conventional analog telephony equipment. FIG. 2 shows a conventional PBX interface. Where appropriate, the same reference numerals will be used to represent the same elements. Here, the CO 500 is coupled directly to a PBX 510; the PBX 510 is typically located at the user's facility. Typically a PBX 510 will only communicate with PBX telephones 508 or with a voice mail system (not shown) or an e-mail gateway (not shown). As is well known, a PBX 510 will only allow communication with devices that are specifically configured for such PBX communication. A PBX 510 will not allow users access to conventional analog telephones 502, analog conference call equipment 503, analog headsets 505, fax machines 504 or analog modem of a computer 506. Similarly, a PBX 510 does not allow access to the internet cloud 516. Likewise, a PBX 510 does not allow a user to utilize different PBX telephones 514 that are configured to operate with other PBX equipment.
Previously, as shown in FIG. 3, at facilities that utilized a PBX for voice communications, additional conventional service lines directly to the CO 500 were required to provide communication to an analog telephones 502, analog conference call equipment 503, analog headsets 505, analog facsimile (fax) machine 504 or to an analog modem of a computer 506. This was because the communication protocols used by a conventional PBX 510 are incompatible for use with analog equipment. Similarly, a PBX 510 of one type could not communicate with PBX telephones 514 of another type because their respective communication protocols were incompatible. A conventional PBX 510 also does not allow VoIP communication via the internet 516 through the PBX.
A two-wire analog telephone set of the type commonly found in the homes of telephone service subscribers typically includes a base unit connected to a central office of a telephone service provider via a bi-directional, two-wire, telephone line and also includes a handset connected to the telephone base unit via a four-wire handset cable. The handset cable has four wires because, for two-way voice communication, the handset includes both a microphone and a speaker, each of which requires a pair of wires. Typically, the telephone base supplies audio signals to the speaker and a DC biasing voltage to the microphone, while the telephone base receives audio signals from the microphone. A two-wire to four-wire converter included in the telephone base unit converts the two central office wires into the four handset wires. In addition, the telephone set includes a ring detector for detecting an AC ring signal provided by the central office and a hook-switch for signaling the central office for answering or placing calls. When the handset is removed from its cradle, the hook switch allows DC loop current to flow from the central office by the telephone set which is detected by the central office.
A conventional modem transmits digital data over a two-wire telephone line by modulating an analog carrier signal according to the digital data. Typically, the digital data is generated by a computer or facsimile machine connected to the modem. The carrier signal is a tone within the frequency range of telephone transmission line. Upon reception by a second modem at the other end of the transmission line, the digital data is reconstructed by demodulating the received signal.
Business organizations often utilize a telephone switching system for providing telephone service to telephone users within the organization. The telephone switching system can have an all-digital interface with its corresponding compatible telephone sets, such as in a digital private branch exchange (PBX). Alternately, the telephone switching system can have an all-analog interface, such as is provided by an analog line card in a PBX or by a central office. In addition, the telephone switching system can provide a combined digital and analog interface with its corresponding compatible telephone sets, such as in a hybrid PBX or a key telephone system (KTS). For the purposes of this document, the term “PBX” is utilized to encompass equipment similar to those above-listed types of telephone switching equipment.
Telephone sets that are compatible with a particular PBX utilized by a business organization are located on the desks of the users. Each PBX-compatible telephone set is connected to the PBX via a corresponding extension line, while the PBX is connected to a telephone service provider via one or more outside lines. The PBX typically includes capability for appropriately connecting incoming calls to the user telephone sets and for connecting outgoing calls from the user telephone sets to an outside line. In this way, fewer than one outside line per telephone set is needed, thus, reducing the cost of the telephone service. In addition, the PBX typically provides a variety of features to the users of the PBX, such as connecting calls among the users and providing voicemail services.
To implement all of the functions of the PBX, certain control and overhead communications must take place between each user's telephone set and the PBX. These communications typically include digital status, initialization and command signals in addition to the two-way voice signals necessary to carry on a telephone conversation. For example, the PBX must know whether a telephone set is connected to a particular extension line in order to know whether or not to route calls to that extension. As another example, the PBX must interact with the user telephone sets in order for the users to receive incoming calls, initiate outgoing calls, terminate telephone calls and to access voicemail and other features of the PBX.
In general, communication protocols utilized for control, overhead and voice communications differ among the various manufacturers of PBX's. In addition, in an all-digital PBX, the voice signals are communicated between the telephone sets and the PBX as digital samples. Thus, analog voice signals are digitally sampled and encoded according to various schemes (e.g. μ-law or A-law) before they are communicated. Upon reception, the digital samples are decoded and converted back into analog voice signals. In a hybrid system, voice signals are communicated as analog signals, while control and overhead communications are digital signals. Therefore, a two-wire analog telephone instrument, such as a modem, fax modem, facsimile machine or teleconferencing device, cannot generally interface directly with a PBX proprietary interface port or line card. Nor can a four-wire analog telephone instrument, such as a headset, handset or modem, generally interface directly with a PBX.
This creates a problem for users of a PBX who wish to use universally available analog telephone instruments, such as modems, fax modems, facsimile machines, teleconferencing devices, headsets or handsets, in addition to their PBX-compatible telephone sets. This problem has intensified by the recent increase in demand for access to the world wide web, which is typically accessed through use of a modem connected to a personal computer. One solution has been to provide a dedicated outside line for each such analog telephone instrument. This solution is not entirely satisfactory, however, because it negates the savings which result from the PBX limiting the number of required outside lines. Another solution has been to provide an analog line card in the PBX and a separate line connecting the two-wire analog telephone instrument to the PBX. This solution can be costly due to the need to install separate extension lines to connect each of the PBX-compatible telephone set and the analog telephone instrument to the PBX.
Another solution has been to provide a device which interfaces a modem with a telephone set through the handset port of the telephone set. For example, U.S. Pat. No. 4,907,267 discloses a modem interface device for use with a telephone set having a base unit and a handset. The telephone set can be a two-wire telephone set or a telephone set designed for use with a PBX. To use the modem interface device, the handset is unplugged from the handset jack of the base and plugged into a handset jack in one end of the device. Extending from the device is a four-wire cable which is connected to the handset jack of the base. The device also includes a modular jack for accepting a two-wire cable which connects the device to a two-wire telephone instrument, such as a modem. A series of switches are manually positioned to select between voice and data communications and to configure the interface device to match the signaling characteristics of the particular telephone set being used.
The manually operable switch arrangement described in U.S. Pat. No. 4,907,267 is improved upon in two products manufactured by Unlimited Systems Corp. of San Diego, Calif. A first of these products, the “KONEXX Office Konnector,” connects to the base of a telephone set and to the handset to provide an interface for a two-wire telephone, facsimile machine or modem. The device detects when the two-wire telephone, facsimile machine or modem is placed off-hook for switching between voice and data communications. A second of these products, the “KONEXX Konference,” is similarly connected between the base and handset, but provides an interface for a teleconferencing device. For each of these devices, a manually operable switch is positioned in one of four positions for adjusting the device to the signalling characteristics of the particular telephone set being used.
The aforementioned interface devices, however, can be inconvenient for interfacing an analog telephone instrument to a PBX. This is because to install such an interface device, the handset cord of a PBX-compatible telephone set must first be disconnected from its base. Then, the interface device must be connected to both the handset and to the base. Next, the analog telephone instrument must be connected to the interface device. Finally, the switch positions for the interface device must be correctly set.
Perhaps a more significant drawback, however, is that each time the analog telephone instrument is used to answer or place a call, the user must manually place the PBX-compatible telephone set off-hook. This is generally accomplished by removing the handset of the PBX-compatible telephone from its cradle. Similarly, when finished using the analog telephone instrument, the user must return the PBX-compatible telephone to its on-hook condition. Otherwise, if the user forgets to return the PBX-compatible telephone to its on-hook condition, incoming calls cannot be connected and will receive a busy indication. In addition, the handset port of the PBX-compatible telephone generally does not provide a ring signal which may be required for automatic answering functions. Another drawback is that some PBX-compatible telephones communicate dialing information via digital bit streams and will not recognize DTMF tones (“dual tone, multi-frequency times as well known in the literature of telephony”) presented at the handset port as dialing commands. Thus, for example, auto-dialing features of an analog device will fail to operate. Therefore, the actual telephone keypad must be used to dial for the analog device. Furthermore, the cables required for connecting such an interface device can become tangled and tend to provide a cluttered appearance on the user's desk.
Therefore, what is needed is a technique for interfacing an analog telephone instrument to a PBX that does not require access to the handset port of a PBX-compatible telephone. What is further needed is such a technique that has sufficient flexibility to adapt to the signaling characteristics of a wide variety of commercially available PBX's. What is still further needed is such a technique that requires a minimum of additional cables to accomplish its functions and that minimizes technical ability required from a user. What is further needed is an apparatus and method that provides users flexibility in selecting among PBX systems, telephone sets and telephony appliances, regardless of manufacturer and have an ability to mix equipment designed to operate according to different protocols. Additionally, what is needed is a method and apparatus that will allow a user to interface any of a plurality of PBX systems to a digital port such as a USB port, ethernet port or the internet, among others.